Oil ring, method for manufacturing oil ring, and piston

Abstract

To provide an oil ring that can regulate the position of an abutment by preventing the oil ring from rotating in the circumferential direction, and can prevent deterioration of the sealing performance between side rails constituting the oil ring and a cylinder, thereby reducing oil consumption.SOLUTION: Each of a pair of side rails 1431, 1431 that constitute an oil ring 143 is formed with a notch 1432 formed on its inner peripheral surface. An expander 1434 has both L-shaped ends that form a pair of bent portions 1435, 1435 bent axially and in opposite directions. One bent portion 1435 is fitted into the notch 1432 of one side rail 1431, and the other bent portion 1435 is fitted into the notch 1432 of the other side rail 1431, and is formed so that when attached to a piston 1, it can fit into an oil return hole 15 formed in an oil ring groove 133 of the piston 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an oil ring, a method for manufacturing the oil ring, and a piston equipped with the oil ring. [Background technology]

[0002] In an engine, when the piston is pushed down by the combustion pressure of the air-fuel mixture, the reciprocating linear motion of the piston is converted into rotational motion via the connecting rod, causing the crankshaft to rotate around the central axis of the main journal.

[0003] The piston is made of, for example, an aluminum alloy and is formed in a generally cylindrical shape. Attached to the outer periphery of the piston, from the piston top (crown) side, are a top ring (compression ring), a second ring (compression ring), and an oil ring. The top ring maintains an airtight seal between the inner wall of the cylinder and the piston, sealing out (preventing leakage of) the high-pressure combustion gas generated in the combustion chamber. Like the top ring, the second ring has the function of preventing gas leakage from the combustion chamber. The oil ring has the function of scraping off excess engine oil and preventing engine oil from entering the combustion chamber.

[0004] As an oil ring, for example, a three-piece type oil ring is widely used, which is formed in a segmented annular shape with a discontinuous portion (a joint) at one location in the circumferential direction, and is composed of a pair of side rails arranged opposite each other, and an expander arranged between the pair of side rails and applying a radially outward biasing force to the pair of side rails (i.e., pressing the pair of side rails against the inner peripheral surface of the cylinder) (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-248730 Summary of the Invention [Problem to be solved by the invention]

[0006] In a horizontally opposed engine, the cylinder and piston are arranged horizontally, so the oil scraped off by the oil ring accumulates below the cylinder (vertically below). If the oil ring rotates circumferentially along the oil ring groove in the piston and the gap in the oil ring (side rail) comes to the underside of the cylinder, the oil that has accumulated below the cylinder can easily enter the combustion chamber through the gap. This can lead to increased oil consumption and the generation of white smoke due to oil combustion during engine startup. Therefore, it is necessary to restrict the circumferential rotation of the oil ring and restrict the position of the gap (i.e., to prevent the gap from coming to the underside of the cylinder).

[0007] Therefore, for example, a circumferential cut is made in the end (the end of the mating surface of the gap) of the side rail that constitutes the oil ring (i.e., the end is divided into an inner peripheral side and an outer peripheral side), the inner peripheral side is bent to form a claw portion, and the claw portion is engaged (locked) with a hole formed on the piston side, thereby prohibiting circumferential rotation of the oil ring and regulating the position of the gap.

[0008] This method prevents the oil ring (side rail) from rotating circumferentially and restricts the position of the gap. However, this method can also deform the outer periphery that contacts the inner periphery of the cylinder when processing the claws (i.e., when bending the inner periphery of the side rail). This can result in a poor seal between the side rail and the cylinder, making it difficult to reduce oil consumption (oil leakage).

[0009] The present invention has been made to solve the above problems, and aims to provide an oil ring that can regulate the position of the gap by preventing the oil ring from rotating circumferentially along the oil ring groove, and that can prevent deterioration of the sealing performance between the side rail that constitutes the oil ring and the cylinder, thereby reducing oil consumption, a method for manufacturing such an oil ring, and a piston equipped with such an oil ring. [Means for solving the problem]

[0010] An oil ring according to one aspect of the present invention comprises a pair of side rails formed in a segmented annular shape and arranged opposite each other, and an expander also formed in a segmented annular shape and disposed so as to be sandwiched between the pair of side rails and which applies a radially outward biasing force to the pair of side rails, wherein each of the pair of side rails has a notch formed in its inner circumferential surface, and the expander has L-shaped ends which form a pair of bent portions bent axially in opposite directions, one bent portion fitting into the notch in one side rail and the other bent portion fitting into the notch in the other side rail, and which is formed so as to be able to fit into an oil return hole formed in an oil ring groove of the piston when attached to the piston.

[0011] According to an oil ring according to one aspect of the present invention, one bent portion of the expander engages with a notch in one side rail, thereby prohibiting relative rotation between the expander and one side rail. Furthermore, the other bent portion of the expander engages with a notch in the other side rail, thereby prohibiting relative rotation between the expander and the other side rail. Furthermore, when the oil ring is attached to a piston, the other bent portion of the expander engages with an oil return hole in the piston, thereby prohibiting relative rotation between the expander and the piston. Therefore, circumferential rotation of the oil ring can be prohibited, thereby restricting the position of the gap. Furthermore, since the machining of the claws of the side rails as described above is unnecessary, deterioration of the sealing performance between the side rails and the cylinder can be prevented. Therefore, oil consumption can be reduced. [Effects of the Invention]

[0012] According to the present invention, the oil ring can be prevented from rotating circumferentially along the oil ring groove, thereby regulating the position of the gap, and deterioration of the sealing performance between the side rail that constitutes the oil ring and the cylinder can be prevented, thereby making it possible to reduce oil consumption. [Brief explanation of the drawings]

[0013] [Figure 1] 2A and 2B are a plan view and a side view of an oil ring according to an embodiment. [Figure 2] FIG. 2 is an enlarged perspective view showing a main part of the oil ring according to the embodiment. [Figure 3] FIG. 2 is an enlarged view (side view) showing a main part of the oil ring according to the embodiment. [Figure 4] 4(a) is a cross-sectional view taken along line IVa-IVa in FIG. 3, and FIG. 4(b) is a cross-sectional view taken along line IVb-IVb in FIG. [Figure 5] FIG. 2 is a perspective view showing a piston incorporating an oil ring according to an embodiment. [Figure 6] 5A to 5C are diagrams illustrating a first manufacturing method of the oil ring according to the embodiment. [Figure 7] 6A to 6C are diagrams illustrating a second manufacturing method of the oil ring according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts will be designated by the same reference numerals. In addition, the same elements will be designated by the same reference numerals in each drawing, and redundant explanations will be omitted.

[0015] First, the configuration of an oil ring 143 according to an embodiment and a piston 1 incorporating the oil ring 143 will be described with reference to FIGS. 1 to 5. FIG. 1 is a plan view and a side view of the oil ring 143. FIG. 2 is an enlarged view (perspective view) of a main part of the oil ring 143. FIG. 3 is an enlarged view (side view) of a main part of the oil ring 143. FIG. 4(a) is a cross-sectional view taken along line IVa-IVa in FIG. 3, and FIG. 4(b) is a cross-sectional view taken along line IVb-IVb in FIG. 3. FIG. 5 is a perspective view showing the piston 1 incorporating the oil ring 143.

[0016] The oil ring 143 is attached to an oil ring groove 133 formed on the outer peripheral surface of the piston 1, which will be described later, and forms an appropriate lubricating oil film on the inner wall surface of the cylinder to facilitate smooth sliding between the cylinder and the piston 1, while also scraping off excess oil to prevent oil from entering the combustion chamber. The oil scraped off by the oil ring 143 is returned to the inside of the piston 1 through an oil return hole 15 (details of which will be described later) formed in the oil ring groove 133.

[0017] The oil ring 143 is formed in a segmented annular shape with a discontinuous portion (a joint 1433) at one location in the circumferential direction and is configured to include a pair of side rails (a first side rail and a second side rail) 1431, 1431 arranged opposite each other, and an expander 1434 also formed in a segmented annular shape, disposed so as to be sandwiched between the pair of side rails 1431, 1431, and applying a biasing force radially outward (outside) to the pair of side rails 1431, 1431 (i.e., biasing the pair of side rails 1431, 1431 radially outward (toward the inner peripheral surface of the piston)). In other words, the oil ring 143 is a three-piece type oil ring.

[0018] More specifically, each side rail 1431 is formed by shaping a strip-shaped wire rod having a substantially rectangular cross section, made of, for example, pressed steel or special cast iron, into a segmented ring shape. The expander 1434 is formed by shaping a strip-shaped wire rod having a substantially rectangular cross section, made of, for example, pressed steel or special cast iron, into a corrugated shape in the axial direction, and then shaping it into a segmented ring shape (axial corrugated expander). The restoring force (repulsion force) of the corrugated wire rod when it is bent into a segmented ring shape serves as a spring force (biasing force).

[0019] In particular, the oil ring 143 prevents the oil ring 143 from rotating circumferentially along the oil ring groove 133, thereby regulating the position of the gaps 1433 and 1436, and also prevents deterioration of the sealing performance between the outer surface of the side rail 1431 that constitutes the oil ring 143 and the inner surface of the cylinder, thereby preventing an increase in oil consumption.

[0020] For this reason, one notch (notch portion) 1432 is formed on the inner peripheral surface of each of the pair of side rails 1431, 1431. The notch 1432 is formed in, for example, a rectangular or elliptical shape so that it can engage with a protrusion of a bent portion 1435 of an expander 1434, which will be described later.

[0021] The expander 1434 is formed in an L-shape (i.e., formed so that the inner peripheral surface side protrudes from the outer peripheral surface side), and both end portions (ends of the mating surfaces of the abutment 1436) are bent (folded back) in the axial direction in opposite directions to form a pair of bent portions 1435, 1435. One bent portion 1435 constituting the pair of bent portions 1435, 1435 is formed so as to be able to fit (engage) with a notch 1432 in one side rail 1431 constituting the pair of side rails 1431, 1431. The other bent portion 1435 is formed so as to be able to fit (engage) with the notch 1432 in one side rail 1431 and with an oil return hole 15 formed in the oil ring groove 133 of the piston 1 (when the oil ring 143 is attached to the piston 1).

[0022] Therefore, the radial length of the inner circumferential projection of the L-shaped bent portion 1435 of the expander 1434 is set to match the depth (radial length) of the notch 1432 of the side rail 1431. Furthermore, the axial length of the inner circumferential projection of the L-shaped bent portion 1435 of the expander 1434 is set in consideration of the thickness of the side rail 1431 and the distance from the oil return hole 15, etc. In other words, the inner circumferential projection (tip) of the L-shaped bent portion 1435 of the expander 1434 is extended in the axial direction so as to be able to fit (engage) with the notch 1432 of the side rail 1431 and the oil return hole 15 of the piston 1.

[0023] One bent portion 1435 is fitted (locked) into the notch 1432 of one side rail 1431. The other bent portion 1435 is fitted (locked) into the notch 1432 of the other side rail 1431. Furthermore, when the oil ring 143 is attached to the piston 1, the other bent portion 1435 is fitted (locked) into the oil return hole 15 formed in the oil ring groove 133 of the piston 1.

[0024] Next, a description will be given of the piston 1 equipped with the above-mentioned oil ring 143. The piston 1 is suitably incorporated into, for example, a horizontally opposed engine.

[0025] The piston 1 is made of, for example, an aluminum alloy and is formed in a substantially cylindrical shape. As shown in Fig. 5, a piston land 11 on the outer peripheral surface of the piston has, for example, three rows of annular piston ring grooves formed along the axial direction. That is, from the piston top (crown surface) side, a top ring groove 131, a second ring groove 132, and an oil ring groove 133 are formed.

[0026] A piston ring is fitted in each piston ring groove. More specifically, a top ring (compression ring) 141 is fitted in the top ring groove 131. The top ring maintains airtightness between the cylinder inner wall and the piston 1 and seals out high-pressure combustion gas generated in the combustion chamber. A second ring (compression ring) 142, which, like the top ring 141, has the function of preventing gas leakage from the combustion chamber, is fitted in the second ring groove 132. The oil ring groove 133 is fitted with the oil ring 143 described above.

[0027] An oil return hole (drain hole) 15 is formed in the oil ring groove 133 of the piston 1 to return the oil scraped off by the oil ring 143 to the inside of the piston 1. A bent portion 1435 of an expander 1434 constituting the oil ring 143 described above is fitted (locked) into the oil return hole 15.

[0028] More specifically, when the piston 1 is assembled into, for example, a horizontally opposed engine, the bent portion 1435 of the expander 1434 is fitted (locked) into the oil return hole 15 so that the joints (joint portions) 1433 of the pair of side rails 1431, 1431 and the joint (joint portion) 1436 of the expander 1434 are not positioned (are not located) below in the vertical direction (near the lowest point). Furthermore, the joints 1433 of one side rail 1431, the joint 1433 of the other side rail 1431, and the joint 1436 of the expander 1434 are arranged so as not to coincide (be offset from each other).

[0029] With the above-described configuration, one bent portion 1435 of expander 1434 engages with notch 1432 of one side rail 1431, thereby prohibiting relative rotation between expander 1434 and one side rail 1431. Furthermore, the other bent portion 1435 of expander 1434 engages with notch 1432 of the other side rail 1431, thereby prohibiting relative rotation between expander 1434 and the other side rail 1431. Furthermore, the other bent portion 1435 of expander 1434 engages with oil return hole 15 of piston 1, thereby prohibiting relative rotation between expander 1434 and piston 1. Therefore, circumferential rotation of oil ring 143 is prohibited, and the positions of joints 1433 and 1436 are regulated. Furthermore, since the above-described processing of the claws of the side rails is unnecessary, deterioration of the sealing performance between side rail 1431 and the cylinder is prevented.

[0030] Next, a method for manufacturing the oil ring 143 (first manufacturing method) will be described with reference to Fig. 5. Fig. 5 is a diagram for explaining the first manufacturing method for the oil ring 143 (side rail 1431).

[0031] (1) First, in the first step (notch step), a notch (notch portion) 1432 is formed at a predetermined interval (the interval of one side rail) on one side of the strip-shaped wire material 140 having an approximately rectangular cross section, for example, using a punch or the like.

[0032] (2) Next, in the second step (winding step), the wire 140 having the notches 1432 formed therein is spirally wound (coiled) around a substantially cylindrical first jig (core jig) 20. On the outer surface of the first jig 20, protrusions 201 corresponding to the notches 1432 of the wire 140 are formed along the axial direction. Then, the wire 140 is spirally wound around the first jig 20 so that the protrusions 201 fit into the notches 1432 of the wire 140.

[0033] Here, the cross-sectional area of ​​the notched portion of the wire 140 is reduced, which reduces the material strength (rigidity), and there is a risk of plastic deformation or distortion occurring when winding the wire 140. Therefore, in the second step, the wire 140 is wound with a substantially cylindrical first jig 20 provided with protrusions 201 corresponding to the notches 1432 of the wire 140. This suppresses deformation due to reduced rigidity of the notches 1432 of the wire 140.

[0034] (3) Subsequently, in the third step (cutting step), the wire 140 wound around the first jig 20 is cut in the axial direction to obtain a plurality of side rails 1431.

[0035] (4) Next, in the fourth process (bending process), a strip-shaped wire having an approximately rectangular cross section is formed into a wave shape, and both L-shaped ends of the wave-shaped wire (expander 1434) are bent in opposite directions to form a pair of bent portions 1435, 1435.

[0036] (5) Then, in the fifth step (attaching step), the expander 1434 is attached (assembled) between the pair of side rails 1431, 1431 so that the bent portions 1435 of the expander 1434 fit (engage) with the notches 1432 of each of the pair of side rails 1431, 1431, that is, so that one bent portion 1435 fits into one notch 1432 and the other bent portion 1435 fits into the other notch 1432. In this manner, the oil ring 143 is obtained.

[0037] Next, a second manufacturing method for the oil ring 143 will be described with reference to Fig. 6. Fig. 6 is a diagram for explaining the second manufacturing method for the oil ring 143 (side rail 1431).

[0038] (1) First, in the first step (winding step), wire 140 (strip-shaped wire 140 having an approximately rectangular cross section) is spirally wound (coiled) around the outer surface of a second jig (core jig) 30, which is approximately cylindrical and has a C-shaped (partially circular) cross section with a discontinuous portion 301 at one point in the circumferential direction.

[0039] (2) Next, in the second step (holding step), the wire 140 wound around the second jig 30 is held down (chucked) from the outside by the third jig 40. Here, since the wire 140 may tend to protrude outward during the notching process described below, the third jig 40 restrains the wire 140 from the outside to prevent the wire 140 from protruding outward (i.e., to prevent the outer periphery of the wire 140 from deforming). As the third jig (holding jig for preventing deformation) 40, for example, a chuck device having multiple (e.g., three) claws or collets attached so as to be movable in the radial direction (capable of reducing or expanding the diameter) can be used.

[0040] (3) Subsequently, in a third step (notching step), with the wire 140 held down from the outside, a notch 1432 is formed in the inner peripheral surface of the spirally wound wire 140 from the discontinuous portion (missing portion) 301 of the substantially cylindrical second jig 30 by, for example, a broach or laser processing. After the notch 1432 is formed in the wire 140, the above-mentioned third jig 40 is removed.

[0041] (4) Next, in the fourth step (cutting step), similar to the third step in the first manufacturing method described above, the wire 140 wound around the second jig 30 is cut in the axial direction to obtain multiple side rails 1431.

[0042] (5) Next, in the fifth step (bending step), similar to the fourth step in the first manufacturing method described above, a strip-shaped wire having an approximately rectangular cross section is formed into a wave shape, and both L-shaped ends of the wave-shaped wire (expander 1434) are bent in opposite directions to form a pair of bent portions 1435, 1435.

[0043] (6) Then, in a sixth step (attaching step), similar to the fifth step in the first manufacturing method described above, the expander 1434 is attached (assembled) between the pair of side rails 1431, 1431 so that the bent portions 1435 of the expander 1434 fit (engage) with the notches 1432 of each of the pair of side rails 1431, 1431, that is, so that one bent portion 1435 fits into one notch 1432 and the other bent portion 1435 fits into the other notch 1432. In this manner, the oil ring 143 is obtained.

[0044] As described above in detail, with the oil ring 143 according to this embodiment, one bent portion 1435 of the expander 1434 engages with the notch 1432 of one side rail 1431, thereby prohibiting relative rotation between the expander 1434 and one side rail 1431. Furthermore, the other bent portion 1435 of the expander 1434 engages with the notch 1432 of the other side rail 1431, thereby prohibiting relative rotation between the expander 1434 and the other side rail 1431. Furthermore, when the oil ring 143 is attached to the piston 1, the other bent portion 1435 of the expander 1434 engages with the oil return hole 15 of the piston 1, thereby prohibiting relative rotation between the expander 1434 and the piston 1. Therefore, circumferential rotation of the oil ring 143 can be prohibited, and the positions of the gaps 1433, 1436 can be regulated. Furthermore, since the above-described processing of the claws of the side rails is not required, it is possible to prevent deterioration of the sealing performance between the side rails 1431 and the cylinder, thereby reducing oil consumption (oil leakage).

[0045] As a result, the oil ring 143 is prevented from rotating circumferentially along the oil ring groove 133, thereby regulating the position of the gaps 1433, 1436, and deterioration of the sealing performance between the side rail 1431 that constitutes the oil ring 143 and the cylinder is prevented, thereby making it possible to reduce oil consumption.

[0046] According to the piston 1 of this embodiment, the oil ring groove 133 to which the oil ring 143 is attached has an oil return hole 15 formed therein, and the bent portion 1435 of the expander 1434 constituting the oil ring 143 is fitted (locked) into the oil return hole 15. Therefore, circumferential rotation of the oil ring 143 along the oil ring groove 133 can be reliably prohibited.

[0047] Furthermore, when the piston 1 according to this embodiment is assembled into, for example, a horizontally opposed engine, the bent portion 1435 of the expander 1434 constituting the oil ring 143 is fitted (locked) into the oil return hole 15 so that the gap 1433 of each of the pair of side rails 1431, 1431 and the gap 1436 of the expander 1434 are not positioned below in the vertical direction. This prevents the gap 1433 of the oil ring 143 (side rail 1431) from being positioned below the cylinder. In other words, it is possible to prevent oil collected below the cylinder from entering the combustion chamber through the gap 1433 of the oil ring 143 (side rail 1431).

[0048] According to this embodiment (first manufacturing method), the wire 140 is spirally wound around a substantially cylindrical first jig 20 having a protrusion 201 formed on its outer surface along the axial direction, so that the notch 1432 of the wire 140 fits into the protrusion 201. This prevents deformation of the wire 140 (side rail 1431) due to a decrease in rigidity of the notch 1432 when the wire 140 is wound. This prevents deterioration of the sealing performance between the outer peripheral surface of the side rail and the inner peripheral surface of the cylinder.

[0049] According to this embodiment (second manufacturing method), the wire 140 wound around the second jig 30 is pressed from the outside, and in this state, the notch 1432 is formed in the inner peripheral surface of the wire 140. Therefore, when the notch 1432 is formed in the wire 140, the wire 140 is prevented from protruding outward, and the outer peripheral portion of the wire 140 (side rail 1431) can be prevented from being deformed. Therefore, it is possible to prevent deterioration of the sealing performance between the outer peripheral surface of the side rail and the inner peripheral surface of the cylinder.

[0050] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and various modifications are possible. For example, in the above embodiments, the piston 1 is incorporated into a horizontally opposed engine, but the present invention can also be applied to, for example, a V-type engine. Furthermore, the present invention can be applied to diesel engines in addition to gasoline engines.

[0051] Furthermore, in the above embodiment, an axially corrugated expander is used as the expander 1434, but an expander of another shape, for example, a coil-shaped expander, may also be used.

[0052] Furthermore, the materials, shapes, dimensions (sizes), and other specific numerical values ​​of the side rail 1431 (notch 1432) and the expander 1434 (bending portion 1435) shown in the above embodiment are examples to facilitate understanding of the present invention, and do not limit the present invention unless otherwise specified. [Explanation of symbols]

[0053] 1 piston 11 Piston Land 131 Top ring groove 132 Second ring groove 133 Oil ring groove 140 Wire rod 141 Top Ring 142 Second Ring 143 Oil Ring 1431 Side rail 1432 Notch (notch) 1433 Joint (joint part) 1434 Expander 1435 Bend section 1436 Joint (joint part) 15 Oil return hole 20 First jig 201 Protrusion 30 Second jig 301 Discontinuity 40 Third jig

Claims

1. a pair of side rails formed in a segmented annular shape and arranged opposite to each other; an expander formed in a segmented annular shape, disposed so as to be sandwiched between the pair of side rails, and applying a biasing force radially outward to the pair of side rails; Each of the pair of side rails has a notch formed on an inner circumferential surface, The expander has two L-shaped end portions that are bent axially in opposite directions to form a pair of bent portions, one bent portion fitting into a notch in one side rail and the other bent portion fitting into a notch in the other side rail, and is formed so that when attached to a piston, they can fit into an oil return hole formed in an oil ring groove of the piston.

2. 2. A method for manufacturing an oil ring according to claim 1, a first step of forming notches at predetermined intervals on one side surface of the wire; a second step of spirally winding the wire around a substantially cylindrical first jig having a protrusion formed on an outer surface thereof along an axial direction so that a notch in the wire fits into the protrusion; a third step of cutting the wound wire rod in the axial direction to obtain side rails; a fourth step of bending both ends of the expander in opposite directions to form bent portions; a fifth step of attaching the expander between the pair of side rails so that the bent portion of the expander fits into the notch of the side rail; A method for manufacturing an oil ring, comprising:

3. 2. A method for manufacturing an oil ring according to claim 1, a first step of spirally winding a wire around an outer peripheral surface of a substantially cylindrical second jig having a C-shaped cross section and a discontinuous portion at one location in the circumferential direction; a second step of pressing the wound wire rod from the outside with a third jig; a third step of forming a notch in an inner peripheral surface of the wound wire rod from the discontinuous portion of the substantially cylindrical second jig while the wire rod is held down from the outside; a fourth step of cutting the wound wire rod in the axial direction to obtain side rails; a fifth step of bending both ends of the expander in opposite directions to form bent portions; a sixth step of attaching the expander between the pair of side rails so that the bent portions of the expander fit into the notches of the side rails; A method for manufacturing an oil ring, comprising:

4. an oil return hole is formed in the oil ring groove in which the oil ring according to claim 1 is mounted; 2. A piston, wherein a bent portion of an expander constituting the oil ring according to claim 1 is fitted into the oil return hole.

5. 5. The piston according to claim 4, wherein when the piston is assembled into a horizontally opposed engine, a bent portion of the expander constituting the oil ring is fitted into the oil return hole so that the gaps of the pair of side rails and the gap of the expander are not positioned below in the vertical direction.

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